The present invention relates generally to compositions and methods for preventing, treating and detecting leishmaniasis, and for stimulating immune responses in patients. The invention is more particularly related to polypeptides comprising an immunogenic portion of a Leishmania antigen or a variant thereof, and to vaccines and pharmaceutical compositions comprising one or more such polypeptides. The vaccines and pharmaceutical compositions may be used, for example, for the prevention and therapy of leishmaniasis, as well as for the detection of Leishmania infection.
Leishmania organisms are intracellular protozoan parasites of macrophages that cause a wide range of clinical diseases in humans and domestic animals, primarily dogs. In some infections, the parasite may lie dormant for many years. In other cases, the host may develop one of a variety of forms of leishmaniasis. For example, the disease may be asymptomatic or may be manifested as subclinical visceral leishmaniasis, which is characterized by mild symptoms of malaise, diarrhea and intermittent hepatomegaly. Patients with subclinical or asymptomatic disease usually have low antibody titers, making the disease difficult to detect with standard techniques. Alternatively, leishmaniasis may be manifested as a cutaneous disease, which is a severe medical problem but is generally self-limiting, or as a highly destructive mucosal disease, which is not self-limiting. Finally, and most seriously, the disease may be manifested as an acute visceral infection involving the spleen, liver and lymph nodes, which, untreated, is generally a fatal disease. Symptoms of acute visceral leishmaniasis include hepatosplenomegaly, fever, leukopenia, anemia and hypergammaglobulinemia.
Leishmaniasis is a serious problem in much of the world, including Brazil, China, East Africa, India and areas of the Middle East. The disease is also endemic in the Mediterranean region, including southern France, Italy, Greece, Spain, Portugal and North Africa. The number of cases of leishmaniasis has increased dramatically in the last 20 years, and millions of cases of this disease now exist worldwide. About 2 million new cases are diagnosed each year, 25% of which are visceral leishmaniasis. There are, however, no vaccines or effective treatments currently available.
Accurate diagnosis of leishmaniasis is frequently difficult to achieve. There are 20 species of Leishmania that infect humans, including L. donovani, L. chagasi, L. infantum, L. major, L. amazonensis, L. braziliensis, L. panamensis, L. mexicana, L. tropica, and L. guyanensis, and there are no distinctive signs or symptoms that unambiguously indicate the presence of Leishmania infection. Parasite detection methods have been used, but such methods are neither sensitive nor clinically practical. Current skin tests typically use whole or lysed parasites. Such tests are generally insensitive, irreproducible and prone to cross-reaction with a variety of other diseases. In addition, the preparations employed in such tests are often unstable. Thus, there is a need for improved methods for the detection of Leishmania infection.
Current experimental vaccines consisting of whole organisms have not proven effective in humans. Accordingly, there remains a need in the art for vaccines to prevent leishmaniasis in humans and dogs, and for improved therapeutic compositions for the treatment of leishmaniasis.
Briefly stated, the present invention provides compositions and methods for preventing, treating and detecting leishmaniasis, as well as for stimulating immune responses in patients. In one aspect, polypeptides are provided which comprise at least an immunogenic portion of a Leishmania antigen, or a variant of such an antigen that differs only in conservative substitutions and/or modifications. In specific embodiments of the invention, the Leishmania antigen comprises an amino acid sequence selected from the group consisting of SEQ ID Nos: 2, 4, 20, 22, 24 and 26. DNA sequences encoding the above polypeptides, recombinant expression vectors comprising these DNA sequences and host cells transformed or transfected with such expression vectors are also provided.
In related aspects, the present invention provides pharmaceutical compositions which comprise one or more of the polypeptides described herein, or a DNA molecule encoding such polypeptides, and a physiologically acceptable carrier. Vaccines which comprise one or more such polypeptides or DNA molecules, together with a non-specific immune response enhancer are also provided. In specific embodiments of these aspects, the Leishmania antigen has an amino acid sequence selected from the group consisting of SEQ ID Nos: 2, 4, 20, 22, 24 and 26.
In still further related embodiments, the pharmaceutical compositions and vaccines comprise at least two different polypeptides, each polypeptide comprising an immunogenic portion of a Leishmania antigen having an amino acid sequence selected from the group consisting of sequences recited in SEQ ID Nos: 2, 4, 6, 8, 10, 20, 22, 24 and 26 and variants thereof that differ only in conservative substitutions and/or modifications.
In other related embodiments, the pharmaceutical compositions and vaccines comprise soluble Leishmania antigens.
In another aspect, the present invention provides methods for inducing protective immunity against leishmaniasis in a patient, comprising administering to a patient a pharmaceutical composition or vaccine as described above.
In further aspects, methods and diagnostic kits are provided for detecting Leishmania infection in a patient. The methods comprise: (a) contacting dermal cells of a patient with a pharmaceutical composition as described above; and (b) detecting an immune response on the patient""s skin, therefrom detecting Leishmania infection in the patient. The diagnostic kits comprise: (a) a pharmaceutical composition as described above; and (b) an apparatus sufficient to contact the pharmaceutical composition with the dermal cells of a patient.
In further aspects, the present invention provides methods for stimulating a cellular and/or humoral immune response in a patient, comprising administering to a patient a pharmaceutical composition or vaccine as described above.
In a related aspect, methods are provided for treating a patient afflicted with a disease responsive to IL-12 stimulation, comprising administering to a patient a pharmaceutical composition or vaccine as described above.